Mostly, the use of an image development machine such as an electro photography copy machine and printer is expanded, particularly digital image scan devices are generally propagated and documents having high quality images and excellent expressiveness are needed, also faultlessness and, moreover, a high quality of printed images are required by supplying and growth of presentation software.
Prior various electro photographic methods are disclosed at U.S. Pat. No. 2,297,691, and Japanese Patent 1968-23910(U.S. Pat. No. 3,666,363) and so on.
Generally, a copy image or a printed image may be obtained by forming an electrostatic latent image on a photosensitive member by various means using photoconductive materials, developing the latent image using a toner and transferring the toner image to a transfer medium such as a paper as occasion demands, and fixing thereof by action of heat, pressure, heat and pressure, or solvent steam. Also, the abovementioned processes are repeated after cleaning the toner left on the photosensitive member without transfer using various means.
Various methods such as the method for developing an electrostatic image using a toner or the method for fixing a toner image are conventionally provided. The toner used for these purposes is generally a grinding toner made as a toner having a desired grain diameter obtained by fusing and mixing colorings consist of a dye or a pigment of thermoplastics and uniformly dispersing thereof, and grinding finely and sorting thereof.
However, while the toner made by the abovementioned method has a good quality, it has some problems in view of imagery quality. For example, the resin composition in which the colorings are dispersed is easily breakable enough to be finely grinded by an economical manufacturing device. However, the resin composition is easy to form particles having a wide grain diameter substantially in fine grinding rapidly, particularly may cause a seriously problem such as document pollution because there are relatively small particles thereof. In this context, while a sorting process is performed in order to remove undesired particles, there is, in this case, a critical problem that it causes high production costs that production yield in manufacturing is low because of wide grain size distribution.
Meanwhile, to solve the problem of the toner made by the grinding methods, Japanese Patent 1962-10231, 1968-10231, 1978-14895 provide the methods for product a toner by suspension polymerization. In the suspension polymerization method, toner particles having a desired grain diameter are obtained by forming monomer composition by uniformly dissolving and dispersing polymerizable monomer, colorings, polymerization starter, if required, cross-linker, charge control agents, and other addition agents, dispersing the monomer composition to aqueous-phase medium including dispersion stabilizer. The method has some advantages that it needs not the breakable property of the resin composition because of having not the grinding step, and can use soft materials, and also that the toner particles has uniform frictional electrification because the colorings does not expose to the surface of the toner particles. Also, the method is very effective in the view of cost reduction such as energy save, production time shortening, process yield improvement, etc. because the sorting step can be omitted.
However, if the grain diameter of the toner is more finer even in the case of using the method, the colorings come easily out the surface of the toner particles so that the performance of the toner will be negatively influenced. Consequently, the method has a disadvantage that the uniform electrification may be degraded and the development capability of the toner may be changed.
The phenomenon is noticeable in case of copy or printing particularly in environment of high temperature and humidity. In relation to that, the method for spreading a resin on the surface layer of the toner particles such as described in Japanese Patent 1988-73277, 1992-35662 is suggested. Though the method may prevent the abovementioned phenomenon affected by colorings by making the thick of the spread layer be thicker, it has a serious problem that absolute value of the quantity of electron charge become smaller because the toner contains little composition having charge controllability. Such problem is being recognized and reported substantially in many case.
To solve the problem, the method for adhering charge control agents to the surface of the toner such as described in Japanese Patent 1990-62666, 1990-273558, and 1994-134437 is suggested. However, the method may cause a serious problem in operation as, in case of repeat of copy or printing, the charge control agents are separated from the surface of the toner particles in view of durability of the toner.
Meanwhile, Japanese Patent 1986-238846, and 1994-197203 disclose the use of an electrostatic image developing toner containing the toner particles made by suspension polymerization method which performs dispersing polymerizable monomer composition containing polyester resin to water-borne medium and assembling thereof. However, it is expected to provide an electrostatic image developing toner having a better friction electrification, multiple operation, heat-resisting offset property and translucency.